Multiplex telephony and telegraphy.



G 0 SQUIER I HULTIPLIBX TELEPHONY AND TELEGRAPHY.

Patented Jan.3,1911r UNITED- STATES GEORGE ownusooiiin; or THE unrrnnSTATES ARMY.

ATENT OFFICE.

MULTIP LEX TELEPHONY AND .TELEGRAPHY.

specification of Letters latent.

Patented an. 3, 1911 Application filed November 5, 1910. serial No.590,804.

(DEDICATED TO THE PUBLIC.)

" ments in Multiplex Telephony and Telegraphy,.of which the following isa specitL- cation;

This application is made under the act of March 3, 1883, chapter 14:3,(U: S. Statute means of wires, .andwhere use is made in this applicationof the term high frequency,

-XXII, p. 625,) and the invention herein described and claimed. may'bcused by the Government of the United States or any of its ofiicers oremployees in the'prosecution 'of work for the United States or by anyperson in the United States without the payment of any royalty thereon;

This invention relates to multiplex telephony and tele'graphy andhas itsobject the simultaneous transmission of a plurality of telephonic andtelegraphic messages over a single circuit.

A further object of the invention is to makeuse of grounded or eartluzd-.;onnections in combination with the usual metallic eircuit.

A further objectis to render such a system as the above silent toexternal disturbances and in such manner as to eliminate all cross talkor harmful effects of one nurssage upon another.

A further object is to apply electric waves of such frequencies as tomake possible the selection and complete ihdependencc of the variousmessages.

A further object is to superimpose upon a. standard battery telephonecircuit, as now commercially in use, one or more. telephonic andtelegraphic circuits .without any inter ference of the various messages.

In accomplishing the above results, use is made of electromagneticivaves, or oscillations, of high frequency, propagated by it isunderstood to mean any ultra-sound .--.frequ'ency"or frequencies abovethe limit of audition.

Reference is here made to my co-pendin applications, Serial Numbers590,801 and 590,802, filed November 5, 1910, in which I havediscussed atlength the advantages and limitations of the use of electromagneticwaves of various frequencies in such systems as described there andhere. In accomplishing the desired results, I heve found it necessaryand suflicient tocornbine the engineering practice of wirelesstelegraphy and telephony with the engineering practice of wiretelegraphy and telephony. I have. also found It necessary, in order toobtain satisfactory results, to make use of such detectors as arecommonly found in the wireless telegraphic hrt. Attempts have been madeat iultiplex telephony, but I have found these inoperative for thereason, among others,

that-no detector or equivalent device has been used. These detectors arenot used because of any greater inherent sensitiveness to electricalenergy than resides in the telephone receiver itself, but lgcause theenergy being in the form of rapid oscillations cannot affect thetelephone or other communicating device.- These rapid oscillations cannot sensibly affect the telephone, because the diaphragm in its" motionmust reverse with the reversal of the current and the deflecting impulseif applied directly to the telephone receiver will be first in onedirection and then in the other with a frequency so high that thediaphragm cannot sensibly follow or respond. Furthermore-if thediaphragm should respond with this frequency the efiect would not, beaudible. Also in the case of the ordinary telephone, on account of thelarge self-inductance of the instrument, the high frequency E. M. F.generated by the waves would produce in the telephone receiver onlyextremely weak currents. I have found it. necessary therefore, andconsider it. an important part of my invention. to make use of some formof integrating detector to transform the rapid oscillations into effectsp'hich can be manifested by the indicating instrument.

This application iselosely related to my three co-pending applications,Serial Numhers 590,801.590302, and 590.803, filed N0- vember 5 1910. Ineach of these, use is p made of high frequency waves as :1 vehiclefrequency circuits 'in parallel between t e ordinary battery line andthe earth.- 'Inthis application I shall describe a manner of conmeetinga plurality of such. high frequency circuits in series relation, makinguse ofthe telephone circuit and ground connections.

In the drawings forrnin a part of this specification, several modications .for c rcuit connectionszare shown, and in said drawings, Figurel illustrates a clrcuit in which a plurality of transmitting or rcceiv-'in .circuits is connected in series in a circult between the ca rth andthe ordinary teleph'one line.

modification of I Referring to these figures in detail, Fig.

Figs. 2, 3 and 4: illustrate a 1 shows a common metallic circuit A-A,

'for ordinary tele bony, across which. are' one sets B B. These brid edthe tele g lhde'the usual apparatusin telephone sets-inc resent use inlocal battery circuits, there ingsho'wn a transmitter 1 of any suitableform'such' as a microphone transmitter with its local battery 2 and theprim ry of the transformer 3. Also there are siown connected in theusual wa the ringing circuit 4, the switchhook 5 an the receiver 6. Thesecondary of the transformer 3 is bridged directly across the line whenthe receiver is off the hook.- The invention is not in an way connectedwith the details of this tele- {16118 connection, an or the usualcircuits ing suitable, and t e one described bein given merely asanillustration. Con'necte to the line wire A, at or near its connectionto the telephone set B, I have shown a circuit connection to the earthat E, this circuit including the variable inductance I, the secondarycoil S, the primary coil. P and the variable condenser C, these .allbeing connected directly in series. Inductively con-- nected to thesecondary S is a primary coil P which is in circuit with the high fruency generator G, thiscirc'uit also inclu ing a variable condenser C,and a microphone M. Indhctively connected to the primary P; is asecondary coils including in its circuit a variable condenser C and avariable inductance L. Shunted around the condensenis the detector D,and opcratively associated with the detector D is the telephone set F,with a battery if desired. At or near the station 13 is a similar earth-connection, including the inductance I, the primary Pf, the secondary Sand the conat the station constructed as to denser C, these being allvariable and connected in series in the same manner as shown at thestation B. Inductively connected to the rimary P, is a receiver circuitIt, simi ar in ever respect to the receiver ll l Inductively connectedto the secondary S is a transmitter circuit T, similar in every respectto the transmitter circuit T at the station B. The receiver It is tunedto the frequency of the oscillations given off by the transmitter T andthe receiver circuit R is tuned to the frequency developed by thetransmitter T, these frequencies being sufiiciently different to afl'ordefl'ective, selective tuning. The tuning elcments throughout thecircuitwhich comprise the various condensers and inductances are allvariable in order to permit of ready and eilective tuning of each andany circuit. The high frequency transformers are all so 've variablecoupling, either by sliding t e one coil within the other, or having onecoil swing within the other, or by any other suitable method well knownin the wireless art.

The operation of the system is as follows: Ordinary telephoniccommunications may be carried on between the stat-ions B and B by thetelephone sets. Simultaneously therewith high .frequency oscillationsmay be impressed on the line A'by the transmitter circuits T and T; bothof these operating at the same time, if desired. These high fre quencyoscillations are modified in'aocordance with speech by the microphone/M,and oscillations transmltted by T are icked up by the receiver R and arerectifie or transformed by the detector D in such-a way as to give areproduction of speech inathe telephone F, all of these being well knownin the art. So also oscillations modified by the microphone M at-thetransmitter circuit T will betranslated into speech at the station R.All of these messages may exist on the sameline at the same time withoutany crosstalk or interference whatsoever. If desired, one ormore'o'f themicrophones M may be replaced by suitable tele phic keys in order thatcommunication y'telegraphy'may be carried on. Obviously this change willnot affect the principle of the operation in any way whatsoever.The-telegraphic signals may be produced by the ordinary key placeddirectly in the generator circuit or by such an arrangement as is shownin Fig. 3 of my co-pending-application, Serial Number 590,801. It. is tobenotcd in this circuit that I have connected a metallic circuit to.earth at both ends, and I have done this tuning elements, also act as acheck to an y earth disturbances in the vicinity. This IS possible onlybecause the condensers- C and C here used are of very small electricaldisunensions, being measured in some thousandths ofa niicrofarad,whereas the condensers now in ordinary use in telephone practice have acapacity measured in microfarads. Such large condensers otlcr very smallimpedance to, the passage of external disturbances of such frequenciesas are within the audible limit, but. with my very small condensers andsharp tuning in the ground circuit to a frequency entirely above 0audition, these low frequency audible disturbances are entirely shutout, giving inc whatchooselo ca ll a silent ground con ncctiou. In viewof the fact that heretofore single line telephone circuits whichinclutlc a ground return, or a 'QAvirc telephone circuit which isgrounded at either end,.arc

subject'to niany and strange noises, the

causes of which are not entirely understood, I consider that in ypresentinvention, whereby a I am enabled to use it groundconnection on asingle telephone circuitv with no such'disturbances, a 'very importantand essential part of my invention. I have found -thc above circuitsentirely successful on a standand telephone line circuit COIlSlSlIlIlgof a pair of twisted copper conductors, pa per insulated, which pairconstitutes but one out: of a large number -iuclosed in a lead sheathused in ordinary city-- tratfic. This lead sheath surrounding the pairof wires brings the earth connection very close indeed to the linecircuit all along its length. but in spite of this. my selectivecircuits are so effective as to give no trace whatsoever of anycrosstall; or influence due -to external disturbances. It isapparentthat any number' of transmitter or receiver circuits may be connerted in series in addition to the two shown in l-ig. 1. i

Fig. 2 shows a modification of Fig. 1 in which a plurality ofearthbrauches are con net-ted in parallel. each single branch connectedto earth being similar in every respect tothe earth'branches shown inFig. 1, and each includingtwo or more circuits which mayi be transmitteror receiver circuits, these circuits being indicated onlydiagrammatically and designated by the reference characters '1 and Rthroughout. The

0 connections of the battery sets B and B are shown onlydiagrammatically. it being nn (lei-stood that the connections aresimilar to those shown 111 Fig. 1. Each transmitter has a differentfrequency always being of ultra-sound frequency. and each transmitterhas a correspnndn'ig receiver circuit at the (.lher endof the line tunedto its frequency.

590,802, cited above.

of my invention. In connection with Fig. i,

I may also use condensers K and K bridged l across the lines A A whichserve the pur pose of placing; the two lines A and A in parallel for thehigh frequency currents. 'l'his capacity, however, is made so small asto give practically insupcrablc impedance to the telephone currents ofordinary frequencics as given by the telephone sets B and B. It is alsoobvious. as shown in Fig. 2, that high fret ueney currents may beconuc'rled to the line wire A as shown at T" and R", these circuitshaving connected in them a plurality of transmitter or receiver"circuits in any suitable arrangement.

Fig. 3 shows a further modification, which is a combination of thesystems shown in Figs. 1 and 2- and thesysteuis shown in my c0- pendingapplication. Serial Number 590,802. In this figure, a plurality ofbranches connected to the earth is shown," each circuit including aplurality of transmitter or receiver circuits, as shown in Fig. 2. I naddition to this highfrequency trans mitter circuits are inductivelyconnected by means .of transformers connected directly in the linecircuit in series with the battery sets B and B in the manner describedin my covpending application, Serial Number In this case, the corndenser-s K and K are necessaryin order to give a free path for the highfrequency as cillations of the series connected transmitter and receiversets f1" and R.

.Fig. at shows a further modification in which the battery sets B and Band one of the line. wires such as A, are entirely eliminated,in whichcase I have multiplex telephony by a single wire using earth return. Asis-apparent'from this Fig. 4, I have shown a plurality of groundbranches, each including a plurality of telephone or re ceiver sets,each transmitter having a different frequency and having a receiver setat the other end of the line tuned to its perio dicity. Also in serieswith the. line, I have connected other transmitter and receiver sets, asshown diagrammatically at T and R. I In this caseI am able to carry onmultiplex telephony by the single wirc'con- -nected to earth at variouspoints without. any cross-talk or disturbances from external causes. andI consider this an essential part- I have shown means whereby Morsetclegraphy. may be. carried on in the. usual way 'nnd-jtliis without anycross interference of the messages. 'In case way stations are used onthe line, each of, such stations will be 120 shunted by a smallcondenser for a -,con denser and inductance tuned to the frequency ofthe highfrequncy oscillations. Thus it is apparent: that my inventionmay be supcl'ii'i'iposed directly on the"prescnt" Morse telegraphsystems. Other forms of.

high frequency transmitter and rcceiver cir-- cuits may be used in placeof those shown,

and various suitable modifications are shown' limited to the exactconnections shown, but

What I claim as my invention is the following:

1. In a silent earthed multiplex telephone and telegraph systei'n, a lne wire; a plurality of earth circuits extending from said line; aplurality of transmitter or receiver circuits associated in seriesrelation breach of said earth circuits, each transmitter 011" cuitimpressing different but ultra-sound frequencies on the line, eachreceiver circuit being tuned to the frequency of one transmitter. i i

2. In a silent earthed multiplex telephone and-telegraph system, a linewire a plurality of earth circuits extending from said line; a pluralityof transmitter or receiver circuits associated. in series relation ineach of said earth circuits, a plurality of transmitter and receivercircuits associated in series in the line, each transmitter impressingdifferent but ultra-sound frequencies on the line, and each receiverbeing tuned to the frequency of one of the transmitters.

3. In a multiplex telephone and telegraph system, a line wire; lowfrequency signaling apparatus connected to the line, a plurality ofround circuits extending from said line, a p urality of transmitter orreceiver circuits associated in series relation in each earthconnection, each transmitter circuit impressing different butultra-sound frequencies on the line, each receiver circuit being tunedto the frequency of one transmitter.

4.,In a multiplex telephone and telegraph system, a pair of line wires;low frequency signaling apparatus associated therewith; a plurality of:earth connections placed between each line and-the earth, a plurality ofhigh frequency signaling circuits associated inseries'in each earthconnection, each transmitter circuit developing oscillations ofdifferent but-ultra-sound frequency and each receiver tuned to onetransmitter circuit.

5. In a multiplex telephone and telegraph system, a pair of line wires;low frequency signaling apparatus bridged across said lines; a pluralityof earth connections placed between each line and the earth, a pluralityof high fretfiiency signaling circuits asso' ciated in series in eachearth connectiom'cach transmitter circuit. developing oscillations ofceiver circuit being tuned to one transmitter circuit and containing adetector for high 55 frequency oscillations and a telephone rcceivcroperatively associated with said do tcetor.

6. In a multiplex telephone and telegraph system, a pair of line wires,battery tccphone sets bridged across said line wires, a plurality ofearth connections )laced between each line and the earth, a p urality ofhigh frequency signaling circuits associated in series in each earthconnection, each trans-t mit-ter circuit developing oscillations ofdifferent frequency, each receiver circuit being tuned to onetransmitter circuit and contain ing a detector for high frequencyoscilla- -tions and a telephone receiver operatively associated withsaid detector.

7. In a multiplex telephone and telegra h' system, a pair of line wires,battery to e-- phone sets bridged across said line wires, a-

plurality of earth connections placed be- 2 tween each line and theearth and containing a variable condenser and a variable inductance, aplurality of high frequency signaling circuits inductively associated inseries in each connection, each transmitter circuit containing agenerator of high frequency oscillations, a variable condenser andmike-- tance for tuning said circuits and a telephone transmitter formodifying said oscillations,

each receiver circuit being tuned to' one of the transmitter circuitsand containing a detector of high frequency oscillations and a telephoneoperatively connected therewith.

8. In a multiplex telephone and telegraph system, a pair of line wires;battery telcphone sets bridged across said 'line wires; a plurality ofearth connections placed between each line and earth and containing avariable inductance, and variable condenser;

a plurality of high frequency signaling cir.-

cults inductively associated in series in each earth connection aplurality of signaling circuits connected inductively in series in thelines, each transmitter circuit developing oscillations of different pltra-sound frequencies and containing a microphone transmitter formodifying. the"oscillations in accordance with speEch,--each receivercircuit coiiltaining a variable inductanceand a variable capacity,

and tuned to thefrequency of one transmitter circuit, a detector inshunt to, thecondenscr of the receiver circuit and a telephoneoperatively connected therewith. Y

9. lira multiplex telephone and telegraph system, a. pair of line wires;battery tele p'hone sets bridged across said line wires;

a condenser small capacity parallel to each of the battery telephonesets; a plurahty of earth connections placed between eachline and earthand containinga vent-" difi'eieiitbut ultra-sound frequency, each reable iriductance. and a variable 'capacity, 'a

plurality of high frequency signaling cit" containing a variableinductance and a vari- 1Q cnits inductively zifitiQCiillQLi in'scries ineach able capacity and' tuned to the frequency of -(IXI'lll connection;:1 plurality of signaling one transmitter circuit, a detector inshuntcircuits connected inductively in series in the 3 to the condenser0f the receiver circuit and 55 lines, each transmitter circuitdeveloping a telephone operatively connected therewith.

electric waves of Llill'ei'ent ultra-sound fre- GEORGE OWEN SQUIER.quencies and containing a nnerephune Lrans- \Vitnesses: lnitter formodifying the oscillations in ac- P. I. VVOLD,

cordance with speech; each receiver circuit R. CRAM.

